It is often desirable to have very precise two-dimensional arrays of collimated light beams coming from optical fibers e.g., for use with an all optical switch. In particular, for single-mode optical fiber, as is typically used in optical communications networks, such fiber often having a core with a diameter of 6–9 microns and a cladding with a diameter of 125 microns, positional tolerances of less than 2 microns from true position and angular tolerances of less than 0.5 degrees are required for each fiber in the fiber array. In the prior art, fiber arrays were made by fabricating a plate into which holes are made, and an individual fiber end is inserted into each hole. The plates may be made from a variety of materials, with silicon or a ceramic being preferred when a very precise array is required. The holes may be made by etching or drilling into the plate, using either mechanical techniques or through the use of a laser. The individual fiber ends are locked into place, e.g., with a small amount of glue. After that, the remaining fiber stubs coming out of the front of the plate are cut off, and the resulting ends are polished flat. Finally an array of lenses is aligned and attached to the fiber array to obtain an array of collimated light beams, each coming from an individual fiber.
Unfortunately, the plates that can be made are usually rather thin, due to limitations in the technology for the plates and their holes. Such a thin plate is able to provide only a rather short guide and hold for each fiber so that, disadvantageously, the mechanical structure of the resulting fiber array is less than desirable. Further disadvantageously, the plates have to be custom-made, which usually requires special tools and expertise. Assembly of the array also requires special skills and precise fixtures. The polishing step at the end of the assembly is not trivial, and it is very time-consuming. Finally, the lens array, a high precision object in itself, has to be carefully aligned and attached to the fiber array.
In U.S. patent applications Ser. Nos. '09/895910 and 09/915964, which are incorporated by reference as if fully set forth herein, certain aspects of the drawbacks of the prior art plate arrangements were overcome but not the difficulty of the alignment of the lens array to the fiber array.
Also in the prior art, fibers have been grouped in bundles for various purposes, e.g., by tying the fibers together or by grouping the fibers inside of a sleeve, e.g., in a fiber cable. However, such groupings do not provide precise alignment and spacing of collimated beams at the exit from the bundle.